The present invention relates to a catalyst used in ammonia synthesis and hydrogen preparation, and the preparation of the same. More particularly, the present invention relates to a chromium-free Fe-based catalyst for CO high-temperature-shift (HTS) reaction, and its preparation.
In conventional Fe-Cr-based catalyst for CO HTS reaction, chromium can improve the activity, heat-resistance and life of the catalyst as a main promoter. However, Cr has been proved to be a potent carcinogen, which can bring harmful effect to human health and the environment in the process of preparation, use and disposal of the catalyst. Accordingly, a great of effort has been directed toward the development of chromium-free catalyst for CO HTS reaction in the whole globe.
The followings are the main developments on the catalyst for CO HTS reaction since 1970""s.
Soviet Union Ivanov Institution has developed a CTKxe2x86x92KC type Fe-Pb-based catalyst, in which another pollutant, Pb, was involved (with Pb in the range of 10-14% by weight).
ICI Incorporation has developed a 71-1 and a 71-2 type chromium-free catalyst comprising CaO, CeO2 and ZrO2(Hf)2). But production process is very complicated, which leads to high cost of the preparation.
Nissan Incorporation has developed a chromium-free catalyst, which is made of Fe2O3, Al2O3, CuO, K2O and Pt.
A patent application entitled xe2x80x9cChromium-free Fe-based catalyst for high(middle)-temperature-shift reaction and its preparationxe2x80x9d (filing number: 95121834.4) filed by China Inner Mongolia Polytechnic University disclosed a NBC type chromium-free catalyst prepared by using Fe2O3, CeO2, Al2O3, and K2O.
However, the catalysts mentioned above have problems, such as complexity of production process, high cost and introduction of new pollutant, which are required to be solved.
It is an object of the present invention to provide a novel chromium-free Fe-based catalyst for CO HTS reaction, which can eliminate the pollution of Cr without introducing new pollutant, and which can be produced simply by using the equipment for producing conventional HTS catalyst. The catalyst comprises FeO, Al, Fe, Si-mixed oxides or aluminum-silicon-sol, vanadium oxides, magnesium oxides, nickel oxides and potassium oxides.
It is another object of the present invention to provide a process for producing the catalyst of the present invention.
The object of the present invent is fulfilled by a novel chromium-free Fe-based catalyst for CO HTS reaction comprising from about 65 to about 90% by weight of Ferriate Oxides, from about 1 to about 10% by weight of Al, Fe, Si-mixed oxides (Al:Fe:Si=6:2:1) or aluminum-silicon-sol (Al:Si=8:2), from about 0.5 about 2.0% by weight of vanadium oxides, from about 0.5 to about 3.0% by weight of magnesium oxides, from about 0.5 to about 3.0% by weight of nickel oxides, and from about 0.1 to about 0.6% by weight of potassium oxides, based on the total weight of the catalytic material.
The present invention further provides a process for producing the catalyst of the present invention. Firstly, a precursor ferric oxides are obtained by the following process. FeSO4.7H2O is dissolved in water at 30-50xc2x0 C., the density of the solution is 1.2-1.35. A (NH4)2CO3 solution (the concentrate of (NH4)2CO3 and NH4OH is 180 g/L-280 g/L and 20 g/L-100 g/L, respectively) is obtained by adding aqueous ammonia solution in NH4HCO3 solution. Then, the FeSO4 solution is neutralized with (NH4)2CO3 solution until pH is between 6.5-7.5 in about 180 minutes at 65-75xc2x0 C. The slushy precipitated product is heated at 90-95xc2x0 C. for 60 minutes, then washed with water at a temperature of 40-60xc2x0 C. for 4-6 times until no white precipitate is produced by adding 10% BaCl2 solution to the water after washing. The final product, i.e. the catalyst of the present invention, is obtained by one of the two methods listed below.
Method 1: All the ingredients except K2O with the amount indicated above are beaten for 30 minutes, followed by pressure-filtering and drying. Then KOH as the precursor of K2O is added. The mixture thus obtained is milled for 60 minutes, followed by graining, and calcining at 300-350xc2x0 C. for 90-120 minutes. Then 0.5%-1.0% graphite is added. The final product is obtained by pelleting the mixture.
Method 2: The slushy precipitated product as obtained above is pressure-filtered and dried, followed by adding all other ingredients with the amount as indicated. Then the mixture is milled for one hour. After that, the mixture is grained, and calcined at 300-350xc2x0 C. for 90-120 minutes. Thereafter, 0.5%-1.0% graphite is added. The final product is obtained by pelleting the mixture.
Upon extensive investigation, the inventors of the present invention are aware that Cr plays a role not only as the structure promoter but also as the electron promoter. Based on this, Al, Fe, Si-mixed oxides (aluminum-silicon-sol) were prepared and these elements were entered into the lattice of Fe3O4, resulting the decrease of the size of the crystallite, increase of the surface area, and substitution for Cr to act as the structure promoter. It was proved by XRD and Mxc3x6ssbauer spectra that vanadium added in the form of vanadium oxides exists as V4+ in A site of the lattice of spinel Fe3O4 in the reaction system. It was also found that nickel oxides added thereto can increase the density of OHxe2x88x92 on the surface of the catalyst, thereby improving the activity and anti-sulfur performance of the catalyst under low stream and gas ratio (ac. 1.85) conditions. Thereby, the performance of the chromium-free Fe-based catalyst of the present invention reached the level of traditional Fe-Cr-based catalyst.